If brightest is what you want, then you'l want one that has a p7 LED, not Q5. Look at this picture here, just a typical comparison between P7 and Q5:
And keep in mind, if you get a p7 flashlight that takes TWO 18650 batteries it will be TWICE as bright compared to one that only takes one. I'm guessing that the p7 light shown in the picture above is only running off 1 18650 battery, so you could imagine how much brighter it would be with two?
So if you want the brightest, I really suggest you get a p7 that takes two 18650's like I did:
http://dealextreme.com/details.dx/sku.14212